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N10-003 Network+ Short Notes

Media and Topologies

  • Centralized computing is an environment in which a mainframe computer provides data storage and computational abilities.
  • Bus topology uses a 10Base2 cable.
  • Bus topology is the easiest to implement.
  • Bus and Ring are zero fault tolerant topologies.
  • Full-mesh topology is the most fault tolerant topology.
  • Mesh topology is a type of physical network design where all devices in a network are connected to each other with many redundant connections.
  • In star topology, when a single connection to one of the network hosts fails, the failed connection will be down and the host will not have network connectivity.
  • LEDs on a network card of a client computer indicates the sending and receiving of data.

  • Ethernet uses CSMA/CD technology.
  • Frame relay is designed to efficiently handle high-speed data over WANs.
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  • Institute of Electrical and Electronics Engineering (IEEE) specification 802.3 defines standards for Ethernet.
  • IEEE 802.11b is an extension of the 802.11 standard. It is used in wireless local area networks (WLANs) and provides 11 Mbps transmission speeds in the bandwidth of 2.4 GHz.
  • The 802.11b wireless standard applies to wireless LANs and provides transmission speeds of up to 11 Mbps in the 2.4 GHz frequency. Its network range is up to 150 feet.
  • CSMA/CD is defined in IEEE 802.3 standard.
  • MultiMode Fiber (MMF) is a type of fiber-optic cable. A fiber optic cable does not require terminators.
  • 802.11 describes a wireless LAN.
  • IEEE 802.5 defines Token Ring.
  • Fiber-optic cable is used for high-speed, high-capacity data transmission. It uses optical fibers to carry digital data signals in the form of modulated pulses of light.
  • Thick Ethernet networks use DB-15 connectors.
  • The maximum segment length of a 10BaseT Ethernet network is 100 meters.
  • 10Base5 can transmit data up to a distance of 500 meters.
  • The maximum segment length that a 1000BaseT network supports is 100 meters.
  • 1000BASE-TX supports the maximum transmission distance of 100 meters.
  • 1000BASE-SX uses a single-mode fiber optic cable.
  • 10GBASE-SR standard uses multimode fiber optic cable.
  • 10GBASE-ER supports the maximum transmission distance of 40km.
  • An unshielded twisted-pair connection uses an RJ-45 connector.
  • RJ-45 connector is used to connect a 10BaseT Ethernet cable to an NIC on a desktop computer.
  • RJ-45 connectors is used to connect a twisted-pair cable to a network adapter card.
  • Speed, expansion, and easy configuration of hardware devices is the prime benefits of using USB.
  • Firewire and USB are serial interfaces.
  • A USB port supports up to 127 devices.
  • 10BaseT Ethernet cable uses 8-pin make connector.
  • RJ-11 connector is used by an analog modem to connect to a phone line.
  • Joystick connector is a 15-pin two row female connector used to connect a Joystick to a computer.
  • A straight tip (ST) connector is a fiber-optic connector used with multimode fiber. An ST connector has a 2.5mm shaft and bayonet locking ring, and allows quick connect and disconnect of 125 micron multi-mode fiber.
  • The MT-RJ and LC connectors can be used with the SFF fiber-optic cables.
  • Multimode fiber optic cable use SC type connectors.
  • F-type connector is required to connect cable modem to the network.
  • SC and ST connectors are old and most common connectors used with fiber optic cables.
  • Both BNC and F-type cables are used with co-axial cables.
  • Fiber-optic cable uses optical fibers to carry digital data signals in the form of modulated pulses of light.
  • The Institute of Electrical and Electronic Engineers (IEEE) formed a project, called Project 802 to help define certain LAN standards. Project 802 defines aspect of the network related to the physical cabling and data transmission, corresponding to the physical and data link layers of Open System Interconnect (OSI) model. The 802 specifications contain twelve different categories. In these specifications, 802.8 defines standards for fiber-optic cable.
  • 100BaseT network uses Cat 5 UTP cables.
  • The maximum length of the cable segment in a 1000BASE-SX network is 550 meters.
  • 100BaseTX cabling can have a maximum segment length of 100 meters.
  • The next step after identifying the probable cause is to take action.
  • Crossover cable is used to directly connect two similar devices.
  • Cat 5e and Cat 6 cables support transmission speed of 1000Mbps.
  • Gateway is a network interconnectivity device that translates different communication protocols and is used to connect dissimilar network technologies.
  • Active hub extends a network on a purely mechanical basis.
  • Routers prevent broadcasts from crossing over subnets.
  • Active hub can resolve the signal strength deterioration problem.
  • To bridge two WAP’s, use Yagi-Uda antennas.
  • To increase the WLAN coverage area, omni directional antennas are used.
  • An active hub repair weak signals, resynchronizes and retransmit data.
  • The brouter can work with both non-routable and routable protocols.
  • A repeater amplifies network signals to extend the distance.
  • 2.4 Ghz spectrum is used by Bluetooth for transmission of data.
  • 802.1X specification defines the authentication method for wireless access.
  • The maximum data transfer rate that can be achieved by implementing the 802.11g wireless standard is 54Mbps.
  • The 802.11g standard, defined by IEEE, is an extension to the 802.11b standard of wireless network. It operates in 2.4-GHz band and brings data rates up to 54Mbps using Orthogonal Frequency-Division Multiplexing (OFDM) technology.
  • An external antenna with the WAP increases the range of the wireless access point.
  • A long length of antenna extension cable and the 2.4GHz interference can affect the range of the network.
  • A vertical antenna is an example of omni directional antenna.
  • An omni directional antenna radiates patterns or signals in all directions.
  • In wireless networks, WAP channel is used to minimize interferences from foreign networks.
  • 801.11a wireless LAN standard is least affected by interference from domestic appliances.
  • The fiber optic cable is immune to EMI.
  • The 801.11a wireless LAN standard is least affected by interference from domestic appliances.
  • 802.11a standard of wireless communication uses OFDM technology for transmitting signals.
  • Performance and range of WLAN is degraded by interferences and solid obstacles such as concrete wall and metal ceiling.
  • Bluetooth uses FHSS transmission method for communication.

Protocols and Standards

  • Media Access Control (MAC) address is a numerical identifier that is unique for each network interface card (NIC). MAC addresses are 48-bit values expressed as twelve hexadecimal digits, usually divided into hyphen-separated pairs: for example, FF-00-F8-32-13-19. A MAC address consists of two parts. The first three pairs are collectively known as the Organizationally Unique Identifier (OUI). The remaining part is known as device ID. The OUI is administered by IEEE. MAC addresses are also referred to as hardware addresses, Ethernet addresses, and universally administered addresses (UAAs).
  • In a MAC address (example- FF-28-3E-AA-A1-26) the first three pairs are collectively known as the Organizationally Unique Identifier (OUI). The remaining part is known as device ID.
  • The last three pairs, in a MAC address, represent the device ID.
  • Session layer of the OSI model manages communication between network entities in a network.
  • Session layer of the OSI model provides dialog management and assists the upper layers in connecting to services on the network.
  • The Transport layer of the OSI model divides a message into smaller segments for the underlying protocols.
  • The Transport layer manages data integration between communication entities in a network.
  • The Transport layer defines the function of TCP and IP.
  • The Session layer of OSI establishes virtual circuit session and provides user authentication.
  • The Physical layer of the OSI model is responsible for packaging and transmitting data on the cable.
  • Network layer performs packet switching and path determination.
  • TCP works at the transport layer of the OSI reference model.
  • Hubs can be replaced by switches to control the network traffic efficiently.
  • A bridge operates at Data-link layer of OSI.
  • The data-link layer of the OSI reference model is responsible for bridging.
  • Intelligent hubs and bridges work at the data link layer of the OSI reference model.
  • RTMP protocol is used by AppleTalk.
  • Novell supports TCP/IP, IPX/SPX, and AppleTalk protocols.
  • COM2 and COM4 use IRQ3 by default.
  • In Windows operating system, General Protection Fault occurs when a program tries to access memory that is currently in use by another program.
  • An IP address has two parts, network ID and host ID.
  • IPv6 addresses are hexadecimal numbers, made up of eight octet pairs. An example of an IPv6 address is 45CF: 6D53: 12CD: AFC7: E654: BB32: 543C: FACE.
  • 127.0.0.1 is a loop-back address.
  • Class A addresses are assigned to networks with large number of hosts. This allows for 126 networks and 16,777,214 hosts per network.
  • Class B addresses are assigned to medium-sized to large-sized networks. This allows for 16,384 networks and 65,534 hosts per network.
  • Class C addresses are used for small networks. This allows for 2,097,152 networks and 254 hosts per network.
  • Class D addresses are reserved for IP multicast addresses. Microsoft supports Class D addresses for applications to multicast data, to multicast-capable hosts, on an internet work.
  • Class E addresses are experimental addresses and are reserved for future use.
  • 255.255.255.255 is the broadcast address for all nodes on a TCP/IP network.
  • TCP/IP uses the node addresses that are divided into classes.
  • Configuring TCP/IP requires three parameters: IP address, subnet mask, and default gateway.
  • Subnetting the network reduces traffic congestion and optimizes the IP address space.
  • Subnetting is used to segment a large network into smaller networks.
  • Private IP addresses can be assigned by many organizations at a time without any conflict, as packets from private addresses are not routed over the Internet. Moreover, these addresses allow users to share a single public IP address.
  • Subnetting is a process through which a TCP/IP network is subdivided by using parts of the node address as network IDs.
  • RFC 1597 has set aside the following address ranges for private use:
    • Class IP Address Range
    Class A 10.0.0.0 to 10.255.255.255
    Class B 172.16.0.0 to 172.31.255.255
    Class C 192.168.0.0 to 192.168.255.255
  • VPN uses L2TP for tunneling.
  • If a Windows 2000 DHCP client is unable to find a DHCP server, the client will automatically assign itself an IP address.
  • To automatically assign IP addresses to each computer on a small private network, you can use the Automatic Private IP Addressing (APIPA) feature of Windows 2000.
  • FTP is the primary TCP/IP protocol used to transfer text and binary files over the Internet.
  • FTP uses port 20 and 21 by default.
  • SMTP is used by e-mail servers to send messages.
  • UDP is a connectionless protocol.
  • Protocol is a set of rules.
  • Hypertext Transfer Protocol (HTTP) is used on the World Wide Web (WWW) to display Hypertext Markup Language (HTML) pages.
  • TCP/IP protocol needs to be bound to the dial-up adapter.
  • SSH protocol uses port 22 by default.
  • POP3 does not support retrieval of encrypted e-mails.
  • There are 65,535 ports available with TCP/IP. Ports 0 to 1023 are labeled as well-known ports.
  • An ephemeral port is used by clients to receive a reply message from servers. When a client computer sends a message to a server by using well-known port numbers, the client computer selects a port number (ephemeral port number) randomly and specifies it in the source port field of the request messages that it transmits. The server reads this value and sends its replies to the client. All values above 1024 are available as ephemeral port numbers.
  • SMTP uses port 25 by default.
  • Telnet uses port 23 by default.
  • POP3 uses TCP port 110 by default.
  • HTTP uses port 80 by default.
  • The following table shows the ports assigned to the protocols by default:
    Protocol Port Number
    SMTP 25
    Telnet 23
    FTP 20, 21
    HTTP 80
    POP3 110
  • UDP port 49 is the default port for TACACS.
  • SNMP uses UDP port 161 by default.
  • TCP port 143 is the default port for Internet Message Access Protocol 4 (IMAP4).
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  • Port 53 is the default port for DNS zone transfer.
  • WINS and LMHOSTS files reduce the use of local IP broadcasts for NetBIOS name resolution, and enable users to easily locate computers on remote networks.
  • UNIX uses DNS for host name resolution.
  • WINS resolves NetBIOS names to IP addresses.
  • If both Unix and Windows computers are there on the network, use DNS for host name resolution.
  • MX record and A record are required to be created in the DNS server to enable the mail server to receive mails from the Internet.
  • ATM uses 53 byte packets to transfer data.
  • T3 lines provide a total data transmission rate of 44.736 Mbps.
  • An OC-3 connection has the data transmission rate of 155.520 Mbps.
  • Basic Rate Interface (BRI) and Primary Rate Interface (BRI) are service levels of ISDN.
  • ISDN and PSTN use dial-up method for Internet connections.
  • When you choose to connect the network to the Internet through a direct connection, such as T1, T3, XDSL, or cable modem, you are required to install and configure an external network adapter.
  • The fiber-optic cable is immune to EMI.
  • Modem, dial-up adapter, and TCP/IP protocol is required to connect to the Internet using a PSTN line.
  • High-speed dial-up is the most unreliable Internet connection to be used to host an e-commerce site.
  • ISDN uses the dial-up method for Internet connection.
  • ISDN BRI connection uses 2 channels to send data.
  • Following are the advantages of ISDN connection over a PSTN connection:
    • It provides a faster connection.
    • It provides end-to-end digital communications.
    • It offers more bandwidth.
  • T3 connection uses 672 channels.
  • ADSL and SDSL are types of Digital Subscriber Line (DSL).
  • Broadband can have multiple signals on the wire at the same time, while baseband can have only one.
  • PPP is a remote access protocol that supports encryption.
  • PPP, SLIP, and PPTP are remote access protocols.
  • L2TP with IPSec (L2TP/IPSec)(a PPP-based site-to-site VPN technology) uses user-level PPP authentication methods and IPSec for computer-level authentication using certificates and data authentication, integrity, and encryption.
  • Exchange Server supports Secure Socket Layer (SSL) for passing credentials. SSL ensures that passwords and e-mail body text remain secure while traveling between client and server.
  • Only users with the correct WEP key can authenticate from the access point of the network.
  • IPSEC is used with a tunneling protocol to provide security.
  • SSL and TLS protocols are used to provide secure communication between a client and a server over the Internet.
  • PPTP and L2TP are tunneling protocols.
  • Configuration of an L2TP VPN connection and an IPSec tunnel between the offices, provides the highest possible encryption for traffic between the offices as well as mutual authentication between the two servers.
  • Shared Key authentication requires the use of the Wired Equivalent Privacy (WEP) algorithm.
  • Use SSL and encrypted authentication to secure the Web server in order to allow only authenticated users to access it.
  • SSL allows the server to authenticate itself to the client by using public-key techniques. It then allows the client and server to cooperate in creating symmetric keys that are used for encryption, decryption, and tamper detection during the SSL session that follows
  • In the SSL model of security, the client always authenticates the server, and the server has the option to authenticate the client. In normal circumstances, Web servers do not authenticate the client during the handshake process.
  • Using the SSL protocol, clients and servers can communicate in a way that prevents eavesdropping and tampering of data on the Internet.
  • L2TP with IPSec needs a certificate authority server (CA server) to generate certificates as well as to check their validity for providing secure communication across both ends of the VPN.
  • SSL ensures a secure connection between a Web browser and a Web server.
  • WEP provides basic security for the wireless network.
  • Password Authentication Protocol (PAP) is a Windows RRAS authentication protocol that uses completely unencrypted passwords. It is the least sophisticated authentication protocol, used mostly when a client calls a server running an operating system other than Windows. PAP uses plain text passwords.
  • To use the smart cards for remote access authentication, you will have to take the following steps:
    • On the remote access client computers, enable the smart card authentication on the dial-up connection.
    • On the Routing and Remote Access server, install a smart card logon certificate.
    • Enable the Extensible Authentication Protocol (EAP) check box.
  • The use of smart cards for user authentication is a strong form of authentication.
  • EAP and smart card goes together most of the times.
  • Kerberos uses the Network Time Protocol (NTP) to synchronize date and time of servers and clients.

Network Implementation

  • Spoofing refers to the emulation of the identity of a network computer by an attacking computer.
  • SYN attack refers to a condition in which a hacker sends a bunch of packets that leave TCP ports half open.
  • Apple has made it easy to integrate Mac OS X Server systems into any network environment by adopting Open Directory, Apple’s standards-based directory, and network authentication services architecture.
  • In order to provide file and print services to the Windows clients, you are required to enable SMB services on the Linux server.
  • RLOGIN is a UNIX command that allows an authorized user to login to other UNIX computers (hosts) on a network.
  • Peer-to-peer is a network model where entities in a network can both request and provide network services.
  • WINIPCFG can be used to check the IP address of a Windows 98 client computer.
  • Media tester is used to test the wires for attenuation.
  • Optical time domain reflectometer is used to test breakage in fiber optic cables.
  • Firewall is a security facility used to protect the network of an organization from external attacks by intruders.
  • Firewall is used to protect the network against unauthorized access.
  • Firewall should be installed between the LAN and the Internet to protect a LAN against external access and misuse.
  • A proxy server enhances the performance of Internet access.
  • Public key and private key is used in asymmetric encryption.
  • Rogue employees and dial-up connections are threats to network security.
  • Packet filtering is a method that allows or restricts the flow of specific types of packets to provide security.
  • To enable email communication, port 25 and 110 should be open.
  • VLAN is used to isolate hosts and segments and to control broadcast traffic.
  • In order to configure a VLAN, switches are used to physically connect the computers.
  • A router is used for communication between the hosts of two different VLANs configured in a network.
  • Inter VLAN communication gets affected if a router connecting VLANs fails.
  • VPN is an example of extranet.
  • An intranet is a private network that is contained within an enterprise. Intranet is used to share company information and computing resources among employees. It is also used to facilitate working in groups and for teleconferencing. An intranet uses TCP/IP, HTTP, and other Internet protocols.
  • Extranet is an area of a Web site, which is available only to selected customers, suppliers, and mobile workers. It allows users limited access to a company’s intranet.
  • The Internet was first used in the late 1960s. It began in the form of ARPANET, which was created by the Advanced Research Projects Agency (ARPA) of the Department of Defense (DOD) in USA. The ARPANET consisted of research universities and military contractors with computers linked by telephone lines.
  • An intranet is a private network that is contained within an enterprise. Intranet is used to share company information and computing resources among employees.
  • Sudden reduction in system resources and Corrupted or missing files are symptoms of a virus attack.
  • Boot sector, network files, and system files are vulnerable to virus attacks.
  • To minimize potential virus attacks, a virus protection program should be installed on each workstation on a network.
  • Raid-1 refers to mirroring.
  • A set of disks configured as a volume set provides maximum space for data storage.
  • Mirroring and duplexing both provide fault tolerance, but the highest level of fault tolerance is in duplexing because duplexing consists of two disk controllers and two disks, whereas disk mirroring is configured with one controller and two disks.
  • You can gain fault-tolerance by using striping with parity. You can also enhance the performance with this configuration. Disk striping with parity is a bit faster and uses less disk space than mirroring or duplexing.
  • The minimum number of hard disk drives required for implementing RAID-5 is three.
  • Full and incremental backup methods clear the archive bit of files after performing backup.
  • A full backup is required for taking a differential backup.
  • RAID 0 creates a stripe set but do not provide data redundancy.
  • Although striping with parity allows for fault-tolerance and excellent speed, using a combination of RAID-5 for your data and mirroring for the log will give you more fault tolerance.

Network Support

  • NSLOOKUP is a tool for diagnosing and troubleshooting Domain Name System (DNS) problems.
  • Both PING and TRACERT use ICMP echo requests to diagnose a TCP/IP configuration.
  • NETSTAT is used to show the state of current TCP/IP connections.
  • NBTSTAT with /c switch is used to list the cache of NetBIOS names and IP addresses.
  • NETSTAT is a command-line utility that displays protocol-related statistics and the state of current TCP/IP connections.
  • PING utility is used to test connectivity with a host on a TCP/IP-based network.
  • PING is used to verify the existence of a host in a network.
  • Telnet enables you to access a UNIX server, using a text-based connection.
  • The TRACERT utility traces the path taken by TCP/IP packets to a remote computer.
  • WINIPCFG is used to display all current TCP/IP network configuration values for a computer running Microsoft TCP/IP.
  • The PING LOCALHOST command is used to verify that TCP/IP is bound correctly to the network adapter by communicating with the loopback address 127.0.0.1.
  • NBTSTAT -n displays the list of local NetBIOS names.
  • IPCONFIG is used to display the current TCP/IP configuration of a computer.
  • PING is used to test connectivity by sending data and receiving it back.
  • The NETSTAT and ROUTE utilities can generate a local static route table.
  • The NETSTAT -s command displays the statistics of each protocol installed in a computer.
  • NBTSTAT -R is used to purge the remote cache name table.
  • The ARP command displays and modifies the IP-to-physical address translation tables used by the Address Resolution Protocol (ARP)
  • The ARP utility is used to display and modify the IP-to-Mac address translation table used by the ARP protocol.
  • The maximum transmission speed supported by 1000BASE-CX network is 1000Mbps.
  • The TRACERT utility tells how many hops (maximum 30) away the target device is.
  • 100% packet lost in output generated through PING shows that there is no connectivity between the source and the destination computer.
  • While troubleshooting network connectivity problem, you should take one step at a time and check for connectivity.
  • In order to access a shared Internet connection, the client computers must be configured with the IP address of the ICS server as a default gateway.
  • The most likely cause of lack of inter-segment communication on a routed network is offline router.
  • Identify the scope of an issue to fix the cause of the issue.
  • The following conditions will cause a complete network failure in Bus topology:
    • An open-ended cable without terminators
    • 75 Ohm terminators at open ends
    • A break in a network cable
  • Event Viewer is used to locate the source of problems by monitoring system logs, security logs, and application logs.
  • If a user is unable to log on to the network, the step towards resolving the issue is to determine whether or not other users are able to log on.
  • Forbidden error messages are received when a client does not have permissions to access a Web page.
  • Configuring client computers to use a WINS server for NetBIOS name resolution reduces the overall network traffic level.
  • If user is unable to connect to a Web server hosted on the Intranet, and if he is able to connect to that Web server by using its IP address, the problem is surely with the host name resolution. This means that DNS is not available.
  • If the router in the network is not BOOTP enabled, you will require to configure a DHCP Relay Agent on remote segment for automatic IP addressing.
  • BNC T connectors, BNC terminators, and BNC barrels are used with coaxial cables.
  • Time Domain Reflectometer (TDR) is used to detect breaks in network cables.
  • In Bus topology, all the computers are connected to each other by a single length of cable with 50 Ohm terminators at both ends.
  • In the Ring topology, the problematic terminal can be removed by using barrel connector to bypass the faulty terminal.
  • Break in a cable in token ring topology collapses total network.
  • A break in a cable in the Star topology affects only the host directly connected to the switch.
  • None of the networking components will be affected if a single link fails in a Mesh topology network.
  • In the bus topology network, a random network connectivity problem can occur because of the following conditions:
    • Improper termination
    • Improper grounding
  • 802.11g WAP uses 2.4GHz range, which is also used by some home appliances, such as microwave ovens. The route cause for interferences.
  • Different WEP keys in a laptop and a wireless access point will prevent the laptop from accessing the wireless network.
  • Any issue with the router directly affects the communication between the segments that are connected through it.
  • Although it may seem obvious, one of the first places to look when troubleshooting logon problems is to verify that the Caps Lock key is off.
  • The first step to resolve a password issue is to make sure that the Caps Lock key is off. This is the most common problem that occurs while logging on to a server. If this does not help, then you should check for the connectivity issues.
  • A forbidden error message means that the user does not have permission to access the page.
  • If pinging the server’s own loopback address fails, it shows that the server’s NIC is not working.
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  • After implementing a solution, the next step of an Administrator is to test the solution.
  • Documenting the problem and solution is the last step in troubleshooting a network problem.